As the production of oil and gas resources has moved into deeper and deeper waters, platform structures have correspondingly become much heavier and more expensive. Deep water structures, which typically refers to structures designed for water over 1000' deep, typically weight, for example, in the tens of thousands of tons. The tremendous weight and size of these structures along with the loading condition they are to withstand makes them quite costly to build with this cost generally measured in the thousands of dollars per ton. Weight is also a major factor in the handling and installatione xpense, thus a general rule of thumb is the less a deep water structure weights, the less costly it is to construct and install.
A good overview of the development of off-shore platforms with special emphasis on deep water structures is found in the article entitled "Design and Construction of Deep Water Jacket Platforms" by Griff C. Lee, Mechanical Engineering April, 1983, pages 26-36. This article discusses the various types of deep water structures along with their construction and utilization. In summary it indicates that fixed platforms have been proven to be the most dependable, cost effective and efficient support system available for offshore drilling and production operations. These platforms are, however, out of necessity, all tremendously heavy and costly to fabricate. Generally, two thirds of the weight of a structure is in its lower one-third, thus improvements in anchoring the structure to the sea bed which reduces the weight of the structure is eagerly desired. Additionally, improvements which reduce the platform load and which eliminate or reduce the amount of surface area exposed to wave action is also highly desired.
It is thus an object of this invention to construct a deep water platform with significantly reduced jacket structure requirements. Anothe robject of this invention is to more efficiently utilize the structural supports of the jacket thereby exposing less surface area to wave action resulting in reduced design wave forces. This reduction in design force will consequently reduce the structural requirements and the weight of the platform. A further object of the invention is to anchor the platform by pilings to the sea floor such that the expensive lower jacket tubing can be designed to support significantly reduced static and dynamic forces, these forces being transfered to the less costly pike steel instead.